Novel production method of gaseous fuels

ABSTRACT

A novel process of producing gas fuel is provided, in which low quality fuel such as coal and various kinds of plastics and resins (polymeric compounds) collected as flame retardant waste are decomposed to gas in supercritical water, so that the resultant gas is effectively utilized as fuel. That is, polymeric compounds and aromatic/condensed-aromatic hydrocarbons are decomposed in supercritical water with ruthenium oxide (IV) as a catalyst. The resultant gas components through the decomposition are collected as gas fuel.

TECHNICAL FIELD OF THE INVENTION

The present invention is related to a method of producing gas fuel, in which low quality fuel such as coal and flame retardant waste such as various plastics and resins are decomposed in supercritical water with a catalyst, so that resultant gas can be utilized as gas fuel.

BACKGROUND TECHNOLOGY

Conventionally, it has been known that some types of plastics (for example, foamed polystyrene) are decomposed in supercritical water without a catalyst. Generally, however, a great majority of plastics and resins (polymeric compounds) are stable even in supercritical water at 500° C. In order to process such compounds in supercritical water, it is necessary to apply an oxidant such as oxygen into water to facilitate the combustion.

When a compound to be processed is burned with the critical water oxidization, only carbon dioxide and water are obtained. Further, depending on an amount of the oxidant, a large amount of carbon may be produced due to imperfect combustion.

While coal is very stable in supercritical water, it is known to be possible to extract oily components depending on a type of coal. However, the extracted oily components have a composition containing a large amount of oxygen, thereby making it difficult to use as fuel.

DISCLOSURE OF THE INVENTION

As described above, it is difficult to decompose a great majority of plastics and synthetic resins, which stays in a stable state, through a simple process in supercritical water. It is also difficult to convert coal to fuel. According to the present invention, such polymeric compounds and aromatic/condensed hydrocarbons are decomposed with ruthenium oxide (IV) as a catalyst to produce gas through the decomposition, so that the gas can be utilized as fuel.

That is, according to the present invention, a novel process of producing gas fuel is provided, in which low quality fuel such as coal and various kinds of plastics and resins (polymeric compounds) collected as waste are decomposed to gas in supercritical water, so that the resultant gas is effectively utilized as fuel.

In the present invention, polymeric compounds and aromatic/condensed hydrocarbons are decomposed in supercritical water with ruthenium oxide (IV) as a catalyst. The resultant gas components through the decomposition are collected as gas fuel.

In the present invention, polymeric compounds and aromatic/condensed hydrocarbons, i.e. materials to be decomposed to obtain gas fuel, are immerged in supercritical water. A reaction occurs in the materials to be decomposed in supercritical water with ruthenium oxide (IV) as a catalyst. As a result, the materials are composed into gas components and organic residue, and the gas component is collected as gas fuel.

In the present invention, the novel method of producing gas fuel includes the following steps. According to a first aspect of the present invention, polymeric compounds and aromatic/condensed hydrocarbons are decomposed in supercritical water with ruthenium oxide (IV) as a catalyst to produce gas components as a result of the decomposition. The gas components, which are produced through the decomposition of the polymeric compounds and aromatic/condensed hydrocarbons, are collected to use as gas fuel.

As described above, conventionally, it is very difficult to decompose various plastics (polystyrene, polyvinylchloride, etc.) and synthetic resins, and low quality fuel such as coal. It is possible to decompose such materials in supercritical water with ruthenium oxide (IV) as a catalyst to generate gas. The resultant gas is combustible gas, and can be collected and stored for the use as fuel. When ruthenium oxide (IV) is used as a catalyst, compounds are decomposed in reductive and oxidative environment. The resultant gas produced through the reductive decomposition is combustible low molecular weight hydrocarbons (mostly methane and a trace amount of ethane and propane) and hydrogen, thereby obtaining high quality gas fuel through the present invention.

Furthermore, as the material to be decomposed, it is possible to decompose industrial waste such as polymeric compounds as well as aromatic/condensed hydrocarbons. For example, it is possible to decompose up to 92% of naphthalene to obtain flammable gas as described above. In addition, the present invention is similarly applicable to coal, which is very stable in supercritical water, and it is possible to convert coal into flammable gas with ruthenium oxide (IV) as a catalyst. In other words, it is possible to modify coal into high quality fuel (low molecular weight hydrocarbons such as methane and hydrogen) without containing harmful metal, and nitrogen and sulfur components.

In the present invention, as the material for obtaining fuel, it is possible to use industrial waste such as plastics and resins, thereby producing gas fuel with low cost and contributing to industrial waste treatment.

According to a second aspect of the present invention, polymeric compounds and aromatic/condensed hydrocarbons, i.e. materials to be decomposed for obtaining gas fuel, are immerged in supercritical water. A reaction occurs in the materials to be decomposed in supercritical water with ruthenium oxide as a catalyst. As a result, the materials are composed into gas components and organic residue, and the gas components are collected as gas fuel. Accordingly, similar to the first aspect of the present invention, it is possible to utilize the resultant gas generated through the decomposition of polymeric compounds and aromatic/condensed hydrocarbons as gas fuel.

Conventionally, it is very difficult to decompose various plastics (polystyrene, polyvinylchloride, etc.) and synthetic resins, and low quality fuel such as coal. It is possible to decompose such materials in supercritical water with ruthenium oxide (IV) as a catalyst to generate gas. The resultant gas is combustible gas, and can be collected and stored for the use as fuel.

According to a third aspect of the present invention, the materials to be processed for obtaining gas fuel include a compound having a polymeric structure such as polyvinylchloride (PVC), fiber reinforced plastics (FRP), Teflon resins (PTFE), polypropylene (PP), polyethylene (PE), polystyrene (PS), and Daiflon (PFA); and a compound having an aromatic ring structure such as naphthalene and coal. That is, such flame retardant materials and low quality fuel are used as the materials to be processed, thereby effectively utilizing materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a gas chromatogram showing low molecular weight hydrocarbons obtained through decomposition of polystyrene;

FIG. 2 is a gas chromatogram showing hydrogen obtained through decomposition of polystyrene;

FIG. 3 is a gas chromatogram showing carbon dioxide obtained through decomposition of polystyrene;

FIG. 4 is a gas chromatogram showing low molecular weight hydrocarbons obtained through decomposition of naphthalene;

FIG. 5 is a gas chromatogram showing hydrogen obtained through decomposition of naphthalene;

FIG. 6 is a gas chromatogram showing carbon dioxide obtained through decomposition of naphthalene;

FIG. 7 is a gas chromatogram showing low molecular weight hydrocarbons obtained through decomposition of Taiheiyo coal;

FIG. 8 is a gas chromatogram showing hydrogen obtained through decomposition of Taiheiyo coal; and

FIG. 9 is a gas chromatogram showing carbon dioxide obtained through decomposition of Taiheiyo coal.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to the present invention, a novel process of producing gas fuel is provided, in which polymeric compounds and aromatics/condensed hydrocarbons are decomposed in supercritical water with ruthenium oxide (IV) RuO₂ as a catalyst, and the resultant gas is collected as gas fuel.

In a critical state, water is heated to 374° C., i.e. a critical temperature, at 22.1 MPa, i.e. a critical pressure. When water is filled in a reactor and heated above 374° C., a pressure is controlled by an amount of water and reaches 22.1 MPa or higher. Water in such a state is called supercritical water. It has been known that decomposition is facilitated in supercritical water.

In the present invention, ruthenium oxide (IV) is used as a catalyst. It has been experimentally confirmed that ruthenium oxide (IV) efficiently decomposes organic compounds in any states of liquid, solid, linear structures and cyclic structures to produce gas in supercritical water. Accordingly, in the present invention, ruthenium oxide (IV) is used as a catalyst for decomposing organic compounds in supercritical water.

Materials to be processed for obtaining gas fuel include a compound having an aromatic ring structure such as naphthalene and coal; and a compound having a polymeric structure such as polyvinylchloride (PVC), fiber reinforced plastics (FRP), Teflon resins (PTFE), polypropylene (PP), polyethylene (PE), polystyrene (PS), and Daiflon (PFA) as flame retardant materials.

As an embodiment, polystyrene as the polymeric compound was decomposed in an experiment, as follows: 100 mg of polystyrene (apparent quantity; 0.960 mmol with —C₈H₈— as a unit), 20 mg of ruthenium oxide (IV), and 3 ml of water were placed in a batch-type supercritical water reactor. After the reactor was sealed, the reactor was heated to conduct a reaction at 450° C. for 2 hours. After cooling, the reactor was connected with a vacuum glass line, and produced gas components were analyzed with on-line gas chromatography. An oily organic residue was extracted using chloroform and collected from a water phase. As a result, 99% of polypropylene was decomposed into gas components, and a trace amount (1.1 mg) of the organic residue remained.

As shown in a gas chromatogram (detector: FID, separation column: PorapakQ, carrier gas: Ar) in FIG. 1, it is confirmed that 61% of polystyrene was converted into methane (4.69 mmol), 0.20% thereof was converted into ethane (0.00756 mmol), and 0.091% thereof was converted into propane (0.00234 mmol). The conversion rates were calculated from a total amount of carbon contained in polystyrene and total amounts of carbon contained in hydrocarbon gases. As shown in a gas chromatogram (detector: FID, separation column: molecular sieve 5A, carrier gas: Ar) in FIG. 1, it is confirmed that a large amount of hydrogen (1.04 mmol) was produced. As shown in a gas chromatogram (detector: TCD, separation column: PorapakQ, carrier gas: Ar) in FIG. 3, it is also confirmed that other gas component was carbon dioxide.

The obtained gases are flammable gases (methane, ethane, propane, hydrogen) and carbon dioxide. Carbon dioxide can be selectively collected through calcium hydroxide solution, thereby imposing no influence on the environment. The organic residue has a trace amount, and it was confirmed that there is no influence on the environment upon processing.

As another embodiment, naphthalene as the aromatic/condensed-aromatic compound was decomposed in an experiment, as follows:

100 mg of naphthalene (0.780 mmol), 20 mg of ruthenium oxide (IV) (RuO₂), and 3 ml of water were placed in a batch-type supercritical water reactor. After the reactor was sealed, the reactor was heated to conduct a reaction at 450° C. for 3 hours. After cooling, the reactor was connected with a vacuum glass line, and produced gas components were analyzed with on-line gas chromatography. An organic residue was extracted using chloroform and collected from a water phase. As a result, 92% of naphthalene was decomposed into gas components, and a trace amount (8.5 mg) of the organic residue remained.

As shown in a gas chromatogram (detector: FID, separation column: PorapakQ, carrier gas: Ar) in FIG. 4, it is confirmed that 47% of naphthalene was converted into methane (3.67 mmol), 0.24% thereof was converted into ethane (0.00946 mmol), and 0.074% thereof was converted into propane (0.00192 mmol). The conversion rates were calculated from a total amount of carbon contained in naphthalene and total amounts of carbon contained in hydrocarbon gases. As shown in a gas chromatogram (detector: FID, separation column: molecular sieve, carrier gas: Ar) in FIG. 5, it is confirmed that a large amount of hydrogen (1.61 mmol) was produced. As shown in a gas chromatogram (detector: TCD, separation column: PorapakQ, carrier gas: Ar) in FIG. 6, it is also confirmed that other gas component was carbon dioxide.

The obtained gases are flammable gases (methane, a trace amount of ethane, a trace amount of propane, hydrogen) and carbon dioxide. Carbon dioxide can be selectively collected through calcium hydroxide solution, thereby imposing no influence on the environment. A trace amount of the organic residue was mainly unreacted naphthalene, and it was confirmed that the organic residue can be used again as the material to be processed.

As a further embodiment, Taiheiyo coal as the low quality fuel was decomposed in an experiment, as follows:

100 mg of Taiheiyo coal, 20 mg of ruthenium oxide (IV) (RuO₂), and 3 ml of water were placed in a batch-type supercritical water reactor. After the reactor was sealed, the reactor was heated to conduct a reaction at 450° C. for 2 hours. After cooling, the reactor was connected with a vacuum glass line, and produced gas components were analyzed with on-line gas chromatography. An organic residue produced from Taiheiyo coal was extracted using chloroform and collected from a water phase.

As shown in a gas chromatogram (detector: FID, separation column: PorapakQ, carrier gas: Ar) in FIG. 7, it is confirmed that 0.609 mmol of methane, 0.0343 mmol of ethane, and 0.0170 mmol of propane were produced from 100 mg of Taiheiyo coal. As shown in a gas chromatogram (detector: FID, separation column: molecular sieve, carrier gas: Ar) in FIG. 8, it is confirmed that a large amount of hydrogen (1.23 mmol) was produced. As shown in a gas chromatogram (detector: TCD, separation column: PorapakQ, carrier gas: Ar) in FIG. 9, it is also confirmed that 1.55 mmol of carbon dioxide was produced. A trace amount (4.4 mg) of an oily organic material was extracted.

The obtained gases are flammable gases (methane, a trace amount of ethane, a trace amount of propane, hydrogen) with no harmful components (nitrogen component, sulfur component or heavy metal). Carbon dioxide can be selectively collected through calcium hydroxide solution, thereby imposing no influence on the environment. A trace amount of the organic residue can be stored in a glass bottle, thereby imposing no negative influence on the environment.

As described above, polystyrene (polymeric compound) and naphthalene (aromatic/condensed-aromatic compound) are converted into low molecular weight hydrocarbons (methane, ethane, propane), and hydrogen is produced. The results indicate that ruthenium oxide (IV) functions as a catalyst of reductive decomposition. Further, the conversion into carbon dioxide indicates that ruthenium oxide (IV) functions as a catalyst of oxidative decomposition. Such conversion of a polymeric compound and an aromatic/condensed into low molecular weight hydrocarbons and generation of hydrogen are quite different characteristics from supercritical water oxidation, in which an organic compound is decomposed through oxidation.

The result of the decomposition of polystyrene indicates that ruthenium oxide (IV) decomposes a polymeric compound, i.e. large linear macromolecules, into low molecular hydrocarbons through reduction and oxidation. Furthermore, the result of the decomposition of naphthalene indicates that an aromatic compound having a stable conjugated ring structure is oxidized, and at the same time, is opened reductively to produce low molecular hydrocarbons. Accordingly, ruthenium oxide (IV) functions as a catalyst for decomposing many organic compounds in supercritical water through reduction and oxidation. 

1. A method of producing gas fuel, comprising: decomposing a polymeric compound or an aromatic/condensed-aromatic compound in supercritical water with ruthenium oxide (IV) as a catalyst, and collecting gas generated from the decomposition as the gas fuel.
 2. A method of producing gas fuel, comprising: immersing a polymeric compound or an aromatic/condensed-aromatic compound in supercritical water as a material to be processed for obtaining the gas fuel, reacting the material to be processed in the supercritical water with ruthenium oxide (IV) as a catalyst to decompose the material to be processed into a gas component and an organic residue, and collecting the gas component as the gas fuel.
 3. A method of producing gas fuel according to claim 1, wherein said polymeric compound is a compound having a polymeric structure including polyvinylchloride (PVC), fiber reinforced plastics (FRP), Teflon resins (PTFE), polypropylene (PP), polyethylene (PE), polystyrene (PS), and Daiflon (PFA), and said aromatic/condensed-aromatic compound is a compound having an aromatic ring structure including naphthalene and coal. 